Deposition and renal handling of urinary electrolytes from rats during spaceflight

To study renal handling of urinary electrolytes from male Fisher 344 rats during spaceflight, waste pads were obtained from cages flown in space and from cages used for ground controls. Pads were obtained from cages in which animals were group-housed (n=6 animals/cage) (Animal Enclosure Module; AEM) for 12 days or individually housed (2 animals/divided cage) (Research Animal Holding Facility; RAHF) for 19 days. Pads were washed, and extracts analyzed for sodium, potassium, chloride, calcium, and creatinine concentrations. It was observed that spaceflight reduced the absolute concentrations of electrolytes deposited onto the pads. When adjustments were made for deposition on all cage surfaces during flight, electrolyte and creatinine concentrations were similar to those of controls. Specifically, there were no differences in the sodium-, potassium-, and chloride-to-creatinine ratios of flight and control animals, suggesting no difference in the renal handling of these electrolytes during spaceflight. The calcium-to-creatinine ratio of urine on flight waste pads was reduced, suggesting an increase in reabsorption. From these analyses, the renal handling of sodium, potassium, and chloride does not appear to be altered in rats during spaceflight, while that of calcium may be. Deposition of urine on all surfaces of the cages during spaceflight should be considered in the design of future animal habitats, and in future analyses of waste pad constituents.